In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for the next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
A MIMO wireless system employs a number (NT) of transmit antennas and a number (NR) of receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS spatial streams, where, for all the practical purposes, NS<=min {NT, NR}. The NS spatial streams may be used to transmit NS independent data streams to achieve greater overall throughput.
It may be desirable that devices in wireless communication systems send and receive large amounts of data within a given bandwidth. It may also desirable that these devices operate efficiently. One way to increase the device efficiency may be to use more efficient amplifiers within the device. However, these efficient amplifiers may introduce additional distortion to transmit signals and cause significant spectral re-growth.
One solution is to operate these amplifiers near the non-linear region and use a pre-distortion device at the input of the amplifier to counteract the distortion introduced to transmit signals by the amplifier.